1. Field of the Invention
The present invention relates to a chemical vapor deposition apparatus and a method thereof, and more particularly, to a chemical vapor deposition apparatus and a method thereof that uniformly form a deposition layer on a wafer.
2. Description of the Related Art
Chemical vapor deposition (CVD) is a process used to form a deposition layer on a wafer. In CVD, the deposition layer is formed by the reaction of gas phase reactants at or near the wafer surface. A CVD process is generally performed by securing a wafer in a chamber in a vacuum state, and by creating a low pressure, high pressure, or plasma environment in the chamber. Then, a process gas is injected into the chamber so that the particles of the process gas are deposited on the wafer. In this deposition method, the process gas is injected into and exhausted from the chamber, thereby creating a flow of process gas in which the substrate is placed.
A CVD apparatus for performing CVD typically includes a shower head or a nozzle for injecting process gas into the chamber, and a pumping assembly for exhausting the process gas from the chamber.
Related to the CVD process, U.S. Pat. No. 6,392,350 discloses a plasma processing method capable of reducing a preheating time. Also, U.S. Pat. No. 6,022,811 discloses a CVD process for evenly forming a depositing layer.
Related to the CVD apparatus, U.S. Pat. Nos. 6,221,770, 5,628,869, and 6,333,269 disclose PECVD (plasma-enhanced CVD) apparatuses that use plasma; and U.S. Pat. No. 6,289,842 discloses an MOCVD (metal organic CVD) apparatus that forms a deposition layer in a low pressure, and a high or low temperature environment.
In the processes and apparatuses of the above patents, the spacing between the shower heads or nozzles and the wafer remains fixed. Therefore, the process gas supplied to the center of the wafer flows along the surface thereof until reaching the edges of the wafer, after which the process gas is exhausted by a vacuum pump. A drawback of this approach is that the deposition layer at the edges of the wafer is thicker than at the center of the wafer.